1. Field of the Invention
The present invention pertains to prepolymers and quasi-prepolymers for use in the preparation of coatings, sealants, etc. More particularly, the present invention concerns prepolymers and quasi-prepolymers useful in the preparation of polyurethane coatings and sealants. Even more particularly, the present invention relates to new prepolymer and quasi-prepolymer compositions derived from diphenylmethane diisocyanates (MDI) and polytetramethylene ether glycols of various molecular weights, which are liquid at temperatures of -20.degree. C. to 15.degree. C.
Numerous prepolymer and quasi-prepolymer compositions are known for use in the manufacture of polyurethane coatings, sealants, etc., as well as other polymeric compounds.
Generally, the most important diisocyanates which are readily available on a large commercial scale are the 4,4'- diphenylmethane diisocyanate and the 2,4'-isomer which melt at 39.degree. C. and 34.5.degree. C. respectively. Liquid diisocyanates are highly useful and attempts have been made to liquify both 4,4'-diphenylmethane diisocyanate and mixtures of 4,4'-diphenylmethane diisocyanate and small amounts of the 2,4'-isomer. A serious drawback to these compositions is that the adducts crystalize anywhere from 5.degree. C. to as high as 25.degree. C., and are difficult to liquify once they have solidified.
Diisocyanate compounds which are the reaction products of a diphenylmethane diisocyanate containing at least 15% by weight of the 2,4'-isomer with either propylene glycol or a poly-1,2-propylene ether glycol are taught in U.S. Pat. No. 4,118,411. These diisocyanate compounds are stable and liquid at -5.degree. C. for at least 48 hours. However, these diisocyanates are not suitable for many purposes requiring storage stable diisocyanates.
U.S. Pat. No. 4,115,429 to Reiff et. al. discloses novel prepolymers and quasi-prepolymers stable at low temperatures which are derived from the reaction of methylene bis(phenylisocyanate) having at least 20 percent by weight up to 70 percent by weight of 2,4'MDI content with polyoxyethylene glycols having molecular weights of from 150 to 1500. However, the polyoxyethylene glycols are hydrophilic segments which may create compatibility problems with other system components.
It is to be appreciated, therefore, that there still exists a need for other prepolymers and quasi-prepolymers which exhibit low temperature stability and which are useful in the preparation of elastomers, coatings, sealants, foams and the like having better end use properties than those based on either polyethylene glycol or polypropylene glycol.